A wide bandwidth pulsar timing machine

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Abstract

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Pulsar timing has turned millisecond pulsars into powerful tools for the study of neutron star physics, time-keeping, astrometry, the interstellar medium and binary systems. It uses millisecond pulsars as probes of the gravitational fields of their companions, of globular clusters and of the Galaxy, and provides information on the dynamics of the solar system. It has also confirmed predictions of general relativity, for which Joe Taylor and Russell Hulse received the 1993 Nobel Prize in Physics. Vasts amounts of information are expected as the current searches continue to discover new millisecond pulsars.

This thesis describes the design and construction of the Caltech Fast Pulsar Timing Machine and some preliminary results at the Parkes Observatory. The FPTM is a wide band timing machine built around a digital correlator for long-term timing stability and has a large observing bandwidth to time millisecond pulsars at high radio frequencies, where propagation effects are minimized.

It is the combination of the 128 MHz bandwidth. the 512 lag digital correlator and the 1024 period phase bins with a minimum size of 2.7 [...] that gives the FPTM its power. The large bandwidth makes new observations of faint pulsars possible above 1 GHz, where current receivers easily provide radio signals with more than 100 MHz of bandwidth. The large number of channels reduces the dispersion smearing of distant millisecond pulsars, which often defines the timing floor in timing systems, and the 1024 phase bins of 2.7 [...] or more ensure that the pulsar profile is adequately sampled.

The FPTM is currently at Parkes Observatory, in Australia, where we are undertaking a long-term precision timing program for millisecond pulsars. We frequently observe the bright binary millisecond pulsar J0437-4715 with sub-microsecond times-of-arrival, and have already found interesting features in the pulse profile that could not be resolved with previous timing systems. Nevertheless, we still find drifts in the timing residuals of as much as a few [...] over several hours which we do not yet understand (even though they are also seen by the other timing system at Parkes!). We are confident that we will solve these residuals and consistently time PSR J0437-4715 at the level of 100 ns or better.

We also present the discovery of J0218+4232, a very luminous binary field millisecond pulsar. Its 2.3 ms pulsations were only detected after an exhaustive search that involved building new hardware.